Radioactive object and method of making same



p 1959 L. M. DORFMAN ETAL 2,903,383

RADIOACTIVE OBJECT AND METHOD OF MAKING SAME Filed April 30, 1958 70 VA 6' U UM PUMP MZ/PCUKY FOR SEAL INVENTORS Le 01: M Dar/man d1" JSIzt' o BY United States Patent RADIOACTIVE OBJECT AND METHOD OF MAKING SAL IE Leon M. Dorfman, Riverside, 11]., and Frederick J. Shipko, Indiana, Pa., assignors to the United States of America as represented by the United States Atomic Energy Commission Application April 30, 1958, Serial No. 732,109 Claims. (Cl. 117-218) This application deals with an article of manufacture, in particular with a solid object coated evenly and completely with a thin layer of beta emissive material. It also deals with a suitable process for making such an article.

Somewhat similar coated objects have been made by other'processes; they have had a number of disadvantages. First, it is very diflicult to get complete and even coverage by most other conceivable methods. Second, adhesion is often a problem; when dry the radioactive material often flakes off or is otherwise lost. This is also true of carbon-14 and strontium-90. Further, strontium- 90 has a very penetrating. radiation, which is highly undesirable for such applications as thickness gauging of low density materials, such as paper.

This the object of this invention to obtain an even coating of radioactive material, particularly material which in spite of its beta radioactivity is in a form that is adherent and therefore able to retain its strength for a reasonably long period of time.

It is also the-object of this invention to obtain a coating of known and reproducible radioactivity on an object rigid enough to handle with reasonable care.

"Further, it is an object of this invention to produce an adherent coating of known radioactivity, emitting soft] beta radiation only, at a minimum of cost. These considerations require the use of tritium rather than carbon- 14, which is more costly by a factor of at least 10, based on the amount of radiation produced.

It is another object of this invention to produce an article of lasting utility consistent with the known decay rate of the radioactive substances. The object should not lose radioactive substance by evaporation, by dusting or by flaking off.

The objects of this invention are obtained by depositing a film of tritiated cnprene on the article by the action of gravity. Such a film has been found to be adherent, stable against thermal decomposition and uniform in distribution. In making this film it is possible to control the rate of deposition so that any thickness desired can be obtained. By regulating the amount and tritium content of tritiated acetylene available to form cuprene, the device is capable of having broad variation in the strength of its radioactivity.

We have discovered that tritiated acetylene polymerizes by self radiation to form a solid adherent film-forming material which adheres to all solid surfaces, and particularly well to metals, glass, and organic plastics. This film-forming material is (C H,T herein called tritiated cuprene where x is the same in ordinary cuprene.

It is only necessary to place the object to be coated at the bottom of a vessel, remove the atmosphere and replace it with a partial pressure of tritiated acetylene. A polymerization takes place at ordinary temperatures (20-25 C.) and the tritiated cuprene is deposited on the surface of the object exposed at the bottom of the vessel. The coating is adherent and evenly distributed.

There are a number of uses for such an article. The

2,903,383 Patented Sept. 8, 1959.

article can be used as a secondary radiation standard for calibrating radioactivity-measuring instruments. For suchuse, of course, it is necessary to know the original strength and the time interval since the measurement of the original strength and calculate the activity on the basis :of its well known decay half-life. A film of the described compound is also useful as a static-electricity-discharging device to be used industrially. This use is shown in the publication, The Atomic Energy Guide Letter, in an issue entitled Radioisotopes, The Wonder Tool. It is to be found at page 14. Another use for such an article is for thickness-monitoring during the process of manufacture of thin tissues such as paper. This use is described in the same publication on page 30.

A further use would be the deposition of such a material on a p-n junction ordinarily used in a transistor, with which it makes intimate contact. The tritium betaintensity can be very high but the particle energy is low enough to avoid damage to the metal. A tritiated cuprene film in the microcurie activity range has been deposited on a germanium wafer, a transistor material, by the process of this invention. In this particular application the wafer was made safe for handling by the application of a plastic spray over the cuprene layer. Another feasible protective arrangement is to place a second p-n junction over the deposited film, thus forming a sandwich and utilizing the radiation from both sides of the active film.

coated or protected by a metal backing. This assembly is then used as a light source for phototube calibration. This coating is accomplished more simply than by a previously described method of synthesizing tritium into the stilbene crystal.

Another important use is as a source of radiation in nuclear batteries of the charge accumulation type. Tritium has been used for this purpose in the form of metal tritides. However, the self-absorption loss has been a serious difiiculty. With the use of tritiated cuprene as the source, self-absorption would be practically nonexistent.

In the accompanying drawing an apparatus is illustrated diagrammatically which is usable for all methods of fabrication described herein.

In this drawing, a separable flask is made from sections of standard glass tapered joint stock in which the straight tube bore is approximately 3 cm. The flask consisted of an outer sleeve section 10 closed at the far end and the closure flattened. The inner joint member 11 was rounded at the far end and an outlet was provided for a manometer tube 12. This manometer tube opened at 13 to a pumping and gas collection storage system (not shown). It bore a constant volume mark 14 near the other end. From the low point 15 of the manometer a tube extends downward and then curves upward to a glass stopcock 16. Above this stopcock is a small glass bulb 17 filled with mercury. The upper end of the glass bulb terminates in a tubulature 18. A wafer 19 to be coated was placed in the bottom of flask 10.

In order to admit or remove gaseous material from the flask a flexible connection is made from the tubulature 18 to an auxiliary vacuum pump (not shown) by means of a thick-walled rubber tube. When the atmosphere above the mercury is exhausted the stopcock is opened and the mercury drawn from the manometer into the bulb 17. When the manometer is to be used as a seal or a pressuremeasuring device air is allowed to enter the tubulature 18 and the stopcock opened allowing mercury to be drawn into the manometer tube 12. The stopcock is closed when one end of the mercury column reaches the mark 14. When used in this way the volume of the flask system is constant. The volume was measured to be 102133 In the following an example is given for illustrative purposes. I

Example I A supply of tritiated acetylene is made stepwise by first producing tritiated water by the action of copper'oxide at 400 C. on a tritium-hydrogen mixture and by then reacting the resultant tritiated water with calcium carbide at room temperature. A:m'ass spectrographic analysis shows that the acetylene contains 12.7 volume percent ordinary acetylene, 49.9% half-tritiated acetylene, and 37.4% completely tritiated acetylene. This is stored in a bulb in the system of Fig. -1.

A platinum disk'2.'5 cm. in'diameter and .025 cm. thick weighing 2.5073 gm. is .placed at the bottom of flask 10. The system is evacuated and a pr'essure'of tritiated'acetylene is admitted and sealed intothe flask by the admission of mercury to the mark 14, where the pressure is =deter- 20 mined. The pressure :is read at 312.75 mm. of mercury, corrected to 25 C. The material is allowed to react at room temperature for four days. At the end-of this time the corrected pressure is found to he 271.33 mm. The remaining gases are pumped away, admitted, the flask opened and the foil removed and weighed. The weight increases by 3.3 mg. The activity-is'measured andfound to be 5.21 curies-of soft 5 activity.

The product was found to be-evenly distributed, evenly radioactive, adherent, and nonvolatile.

Similarly another type of radioactive cuprene, emitting 5 particles, may be made by the radiation induced .polymerization of carbon-l4-bearing acetylene, wherein the radiation initiating the polymerization is that caused by the decay of the carbon-14. In such case the acetylene must be made by hydrolysis of calcium carbide in which part of the carbon is radioactive carbon-l4.

It will be understood that this invention is not belimited to the details given herein but that it may be modified within the scope of the appended claims.

What is claimed is:

1. An article of manufacture comprising a solid body,

4 a layer on said body of a substance capableof producing scintillations under B particle bombardment between said body and said coating, and an adherent coating of tritiated cuprene on said layer.

2. The article of claim 1 in which the solid body is in the form of a wafer.

3. The article of claim 2 wherein the wafer is metallic.

4. The article of claim 2 wherein the wafer is glass.

5. The article of claim 2 wherein the wafer is of a polymerized organic plastic material.

6. The article of claim 1 wherein the intermediate layer is anthracene.

7. The article of claim 6 wherein the intermediate layer is stilbene.

8. A process for making a solid body having an adherent coating of tritiated cuprene, comprising positioning the body, with the surface to be coated facing upward, at

a the bottomof a vessel, introducing an atmospherecontaining a large fraction of tritiated acetylene whereby. tritiated cuprene forms by polymerizing action, and allowing the References Cited in the file of this patent UNITED STATES PATENTS 1,537,777 Liedtke May 12, 1925 1,718,626 Bleecker June 25, 1929 2,662,034 Mason Dee. 8,:1'953 2,743,264

Buselli Apr. 24, "1956 OTHER REFERENCES Chemical Reviews, June 1956, v51. 56, No. 3, p 479481.

W. G. Brown: Tritium as a Tool for Industrial and Chemical Research, Peaceful Uses of Atomic Energy," V01. 15, 19 56. 

1. AN ARTICLE OF MANUFACTURE COMPRISING A SOLID BODY, A LAYER ON SAID BODY OF A SUBSTANCE CAPABLE OF PRODUCING SCINTILLATIONS UNDER B PARTICLE BOMBARDMENT BETWEEN SAID BODY AND SAID COATING, AND AN ADHERENT COATING OF TRITIATED CUPRENE OF SAID LAYER. 